1. Field of the Invention
The present invention concerns a method and device for detecting the optical properties of a sample, such as a colorimetric variation obtained during a chemical and/or biological analysis process.
It applies in particular to detecting the presence or absence of micro-organisms, such as bacteria or yeast in a sample of a biological material.
2. Description of the Prior Art
In particular, but not exclusively, it is suitable for a detection of this type in a biological analysis process as described in the application WO 96/29427 comprising a separation phase xe2x80x9con gelxe2x80x9d consisting of:
introducing a sample into a centrifugation tube above a gelled system previously introduced into the tube, this system being designed so as to separate the micro-organisms present in the sample according to their size and including a culture medium favouring the development of the micro-organisms and a reactive agent able to induce a detectable optical measurement variation;
hydro-extract the contents of the tube so as to provoke migration of the micro-organisms present in the sample in the gelled system and promote their development;
show the presence or absence of the micro-organisms in said system via a detection of said optical measurement variation.
Up until now, this detection has been carried out visually and thus comprised all the drawbacks inherent in this type of detection.
The invention can also be applied in other fields, especially in hemostasis. Thus, it can be used in a method to measure blood coagulation time, as described in the patent U.S. Pat. No. 4,918,984 filed in the name of the Serbio company, and includes a densitometric measurement coupled to a determination of the coagulation time of a blood plasma sample. In this example, these two measurements are obtained with the aid of a device including on both sides of a transparent receptacle the sample firstly a lighting device, and secondly a photodetector in front of which an optical passband filter is placed, this photodetector being connected to an electronic processing circuit.
Subsequently so as to improve this device, the following has in addition been provided:
firstly a filtering device including several mobile light filters able to be successively brought into the path of the light beam emitted by the incandescent lamp (lighting device), and
secondly a sampling circuit able to take samples of the measurement signal delivered by the photodetector in synchronism with the running off of the filters and able to associate with each sample an identifier corresponding to the filter used during sampling.
In theory, this solution is able to follow up in real time the variations of the beam detected for each of the wavelength ranges of the filters.
In reality, it does not make it possible to obtain satisfactory results, mainly on account of the run off period of the filters, said period remaining relatively long (without it being able to be reduced) and which results in one sampling in a periodicity of about 2 secs. It is clear that, having regard to this periodicity and the time shift of the detected signals, the comparisons made between these signals becomes dubious and in any event error concerning localisation of the bend remains relatively significant. In addition, owing to the electromechanical portion it introduces, this solution is relatively expensive and requires relatively costly maintenance.
The object of the invention is thus to resolve these problems of slowness and costly mechanical elements and maintenance.
Thus, the invention concerns a static type method requiring no maintenance and consists of carrying out during a relatively short period of timer of about one millisecond to about ten milliseconds an operational sequence including the following stages:
a first exposing of the sample to a first incident light pulse whose light waves are included in a first range of frequencies, this pulse being emitted by a first opto-electronic light source,
a first turbidimetric measurement by a first opto-electronic detector situated approximately in the axis of said incident pulse of the light intensity transmitted from said pulse after passing through said sample,
the storing of the result of this first measurement in a memory,
exposing the sample to a second incident light pulse having approximately the same incidence as the first and whose light waves are included in a second range of frequencies, this pulse being emitted by a second opto-electronic light source,
a second turbidimetric measurement by said first detector of the light intensity of said second pulse after its passage through said sample,
storing in said memory the result of this second measurement.
Advantageously, the duration of said light pulses could be from one tenth of a millisecond to several milliseconds.
In addition, this method includes, during or after said period, the analysis of the results stored in said memory. Advantageously, said detector shall be of the spectrophotographic type so as to be able to measure the fluorescence of the sample.
This fluorescence measurement could in addition be conjugated with a nephelometric analysis taking into account the optical diffusion properties of the sample.
Thus, in the case when detecting the presence of bacteria, it becomes possible to produce a truth table for exploiting the optical property variations of the sample measured by the detectors and deduce from this an indication of the size of the bacteria population, it being understood that:
a slightly higher amount of bacteria is expressed by fluorescence,
an increase of the bacteria generates a reduction of fluorescence, the sample becoming transparent,
a high amount of bacteria generates a non-transparent and non-fluorescent state able to be detected by the nephelometric measurement.
By means of these arrangements, the various measurements, which are virtually simultaneous (extremely short measuring period) are carried out in the same conditions and thus are extremely reliable. In addition, the interpretation of the measurement results is much more random and false negatives are no longer possible.